Regioisomeric thieno[3,4-d]thiazole-based A-Q-D-Q-A-type NIR acceptors for efficient non-fullerene organic solar cells

This study explores the potential of regioisomeric quinoidal-resonance π-spacers in designing near-infrared (NIR) non-fullerene acceptors (NFAs) for high-performance organic solar cell devices. Adopting thienothiazole as the π-spacer, two new isomeric A-Q-D-Q-A NFAs, TzN-S and TzS-S, are designed and synthesized. Both NFAs demonstrate a broad spectral response extended to the NIR region. However, they exhibit different photovoltaic properties when they were mixed with the PCE10 donor to fabricate respective solar cells. The optimal device of TzS-S achieves a PCE of 10.75%, much higher than that of TzN-S based ones (6.13%). The more favorable energetic offset and better molecular packing contribute to the better charge generation and transport, which explains the relative superiority of TzS-S NFA. This work sheds new light on the regioisomeric effect of component materials for optoelectronic applications.

Hole-only and electron-only devices were prepared as ITO/PEDOT:PSS/PCE10:acceptor/MoO 3 /Ag and ITO/ZnO Sg/PCE10:acceptors/PDINN/Ag, respectively.The charge carrier mobility of each blend film, was measured using following expression: In the equation, J is the current density, ε 0 is the permittivity of free space, εr is the dielectric constant of the materials, µ is the charge carrier mobility, L is the thickness of the active layer and V is the internal voltage in the device, and V = Vappl -Vbi, where Vappl is the applied voltage to the device, Vbi is the built-in voltage due to the relative work function difference of the two electrodes.
Grazing incident wide-angle X-ray scattering (GIWAXS) was performed at the National Center for Nanoscience and Technology (NCNST), China.Following sample preparation on Si/PEDOT:PSS substrates, the measurements were taken using XEUSS, WAXS/SAXS system.The sample was irradiated at a fixed incident angle (αi) on the order of 0.18 with an X-ray energy of 8 KeV (X-ray wavelength  = 0.154 nm), and the GIWAXS patterns were recorded with a 2D image detector (PILATUS R 300K) with the sample-to-detector distances of 130 mm.Surface morphology of the films was collected with Bruker Multi-Mode 8 atomic force microscope (AFM) at a Peak-force tapping mode with SCANASYST-AIR probe (force constant of 0.4 N m -1 , tip radius of 2 nm, and resonant frequency around 100 kHz).
The UPS measurement was performed on an Axis Ultra DLD (Kratos, UK) spectrometer with an unfiltered He I (21.22 eV) excitation source and a pass energy of 5 eV.The base pressures of the analysis chamber was better than 5 ×10 −10 Torr.A bias voltage of -9 V was applied to the sample for obtaining the secondary electrons cut-off (SECO) region.The Fermi level (EF) was calibrated from a UPS spectrum using Ar + sputtered clean Au substrate.The LEIPS measurement was performed on a customized ULVAC-PHI LEIPS instrument with Bremsstrahlung isochromatic mode.

Preparation of ZnO Precursor Solution
i) KOH (56.01 g/mol * 13.5 mmol * 1.7 equiv) in 65 mL methanol, was added dropwise (in ten minutes) into the flask containing zinc acetate dihydrate (219.51 g/mol * 13.5 mmol * 1.0 equiv) in MeOH (125 mL) at 65°C.Aftert 2h and 15 min, stirring was stopped and the mixture was aged at RT for 2h.MeOH was decanted and the white precipitates of ZnO nanoparticles (ZnO NPs) were sonicated with methanol three times to remove the reaction residues.Finally, the ZnO NPs were suspended in methanol and the concentration was found to be 21 mg/mL. 2,3 he thus-prepared ZnO NPS (30 L) were statically dispensed onto the cleaned ITO substrates at 2000 rpm and annealed at 130 C for 10 min, prior to the transfer of subtrates into glove box for OSC device preparation.

Figure S1 .
Figure S1.Stokes shift obtained from emission and absorption spectra of TzN-S (a) and TS-S (b) in thin film state.

Table S1 .
Electrochmical parameters, extracted from voltammograms of the materials understudy.

Table S2 .
Photovoltaic performance of OSC devices a with different D:A blend ratio

Table S3 .
Photovoltaic performance of OSC devices a with different D:A blend ratio

Table S4 .
Photovoltaic performance of OSC devices a under varying annealing conditions The average values and standard deviations in parentheses, represent the statistical data obtained from eight and b eighteen independent cells.

Table S5 .
Photovoltaic performance of OSC devices a under varying annealing conditions a Conventional architecture: ITO/PEDOT:PSS/PCE10:TzN-S/PDINN/Ag; The average values and standard deviations in parentheses, represent the statistical data obtained from eight and b eighteen independent cells.

Table S6 .
Photovoltaic performance of OSC devices a with different additives under different annealing conditions Conventional architecture: ITO/PEDOT:PSS/PCE10:TzS-S/PDINN/Ag; The average values and standard deviations in parentheses, represent the statistical data obtained from eight and b eighteen independent cells. a

Table S10 .
Photovoltaic performance of devices a with ZnO NPs (22 mg/mL) as ETL Inverted architecture: ITO/ZnO NPs/PCE10:TzN-S/MoO 3 /Ag; The average values and standard deviations in parentheses, represent the statistical data obtained from eight independent cells. a

Table S11 .
Photovoltaic performance of devices a with PM6 as donor material a Conventional architecture: ITO/PEDOT:PSS/PM6:TzS-S/PDINN/Ag; The average values and standard deviations in parentheses, represent the statistical data obtained from eight and b eighteen independent cells.

Table S12 .
Photovoltaic performance of devices a with PM6 as donor material a Conventional architecture: ITO/PEDOT:PSS/PM6:TzN-S/PDINN/Ag; The average values and standard deviations in parentheses, represent the statistical data obtained from eight independent cells.

Table S13 .
Charge carrier mobilities of newly synthesized regiomeric acceptor materials AcceptorsElectron Mobility ( e ) a Hole Mobility

Table S14 .
V OC and the calculated E loss of devices prepared from PCE10 and two acceptors a a E loss is defined as E loss = E g ˗ eV OC , where E g is the lowest optical bandgap of the donor or acceptor component.